Carbon nanotubes (CNT), including multi-walled carbon nanotubes (MWCNT), few-walled carbon nanotubes (FWCNT), double-walled carbon nanotubes (DWCNT) and single-walled carbon nanotubes (SWCNT), have the best mechanical, electrical and thermal properties of any known material. These properties make CNT an attractive property enhancer for various matrices including polymers. However, owing to the strong van der Waals interactions (of the order of 0.5 eV per nm for SWCNT) which make CNT, especially SWCNT, self-assemble into bundles and, to their general chemical inertness, CNT are practically insoluble (or have very limited solubility) in all common solvents. This lack of solubility makes incorporation of CNT into various matrices including polymers extremely difficult. The interfacial problem that is the lack of compatibility between CNT and the matrices is an issue that still remains to be resolved in composite sciences.
With a view to improving compatibility of CNT in polymer matrices, there have been many attempts in the literature at covalent sidewall functionalization of CNT. One example is as follows (Bahr 2001; Dyke 2003):SWCNT+4-substituted-aniline+isoamyl nitrite→SWCNT-Ph-R
In a second example (Nayak 2007), the authors claim the formation of a C—N bond on SWCNT surface in a solvent-free reaction which results in the attachment of a vinyl moiety on the CNT sidewall as follows:SWCNT+4-vinylaniline+sodium nitrite→SWCNT-N═N-Ph-vinylThe SWCNT-N═N-Ph-vinyl product is isolated with a view to doing more chemistry on the vinyl moiety, and does not suggest that controlled polymerization is achievable without first isolating the SWCNT-N═N-Ph-vinyl product.
In a third example (Nayak 2008), Friedel-Crafts acylation involving a —COCl-substituted SWCNT and styrene in the presence of ZnO also results in attachment of a vinyl moiety on the CNT sidewall as follows:SWCNT-COCl+Ph-vinyl→SWCNT-C(O)-Ph-vinyl
In a fourth example (Simard 2008), a free radical initiated polymerization reaction permits linking an epoxy group to a carbon nanotube through a polymerized bridging agent such as polystyrene or poly(methylmethacrylate).
In a fifth example (Guan 2008), an epoxy substituted molecule may be directly bound the surface of CNT by first priming the surface of CNT with negatively charged groups and then reacting the epoxy compound with the negatively charged CNT.
It is also known that CNT may be coated with polystyrene or copolymers of polystyrene in different ways (Hill 2002; Choi 2005).
However, none of the above attempts or other attempts in the prior art has satisfactorily addressed the issue of polymer-CNT compatibility in polymer nanocomposites.